Yes, unfortunately, there are these S***t Disturbers that upset the tranquility of a house. I think what you're dong is the best solution by keeping kitties separated from her. I would go a little further when she goes to their door and growls and hisses. I would go after her with a stern "No!" and stamp my feet as I walked toward her. This tells her that you disapprove of her bully behaviour. Have had bully cats before, and found it works for me. On the other hand, most of it is jealousy, and I would give SP some extra one-on-one cuddling, and lavish praise on her when she is being a good girl.

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"We humans are indeed fortunate if we happen to be chosen to be owned by a cat." -- Anonymous